The technical field of the present invention is generally the field of tobacco processing, and is more particularly the field of separating and classifying tobacco according to particle size, and of removing impurities from tobacco.
Cut tobacco intended for use as cigarette filler often contains impurities that, if not removed, can lower the quality of a cigarette made from the tobacco. Such impurities include sand and other nontobacco particles. Small pieces of stem, produced when the tobacco is cut into long, thin pieces of filler, can also reduce the quality of cigarettes produced from the tobacco.
Many devices for classifying tobacco according to particle size and weight are known. Such devices, however, tend to damage the tobacco while processing it. Indeed, with expanded tobacco and other delicate materials, degradation of the product is virtually inevitable with conventional machines. In addition, many such devices are not efficient enough to extract the maximum amount of usable filler in only one or two passes, requiring that some fraction of the tobacco be processed as many as eight or ten times before a satisfactory degree of separation is achieved.
It is the object of the invention to provide a method and apparatus for separating and classifying tobacco, especially cut tobacco filler, whole leaf tobacco and expanded tobacco, according to particle size, weight and shape.
It is another object of the invention to provide such a method and apparatus in which the tobacco is processed without passing through a winnower or an air lock.
It is another object of the invention to provide such a method and apparatus capable of processing very delicate material, such as expanded tobacco, without significant degradation of the material.
It is still another object of the invention to provide such a method and apparatus that use a stream of air for separation and that require a lower maximum air speed than is common in conventional air separators.
It is another object of the invention to provide such a method and apparatus that produce a lower level of noise than do conventional air separators.
It is yet another object of the invention to provide such a method and apparatus that can separate two classes of material differing only slightly in their characteristics.